It is known that many aircraft, in particular civil transport aircraft, are equipped with a collision warning device making it possible to transmit a warning signal in the case of risk of collision of the aircraft with the terrain. With regard to the collision warning device, it can be in particular a device of the TAWS (“Terrain Awareness and Warning System”) type, of the EGPWS (“Enhanced Ground Proximity Warning System”) type or of the GCAS (“Ground Collision Avoidance System”) type.
Such a collision warning device is generally capable of generating two warning signals relating to different warning levels, namely a caution and a warning. Generally, a caution is transmitted about 60 seconds before a potential collision of the aircraft with the terrain, when the risk of such a collision is detected. If this collision risk is still beyond doubt about 30 seconds before the predicted impact of the aircraft with the terrain, the said warning device transmits a warning. In the case of a warning, the pilot must of course react immediately. On the other hand, in the case of a caution, the pilot or pilots are supposed to verify the reality of the potential risk of collision with the terrain and to modify his flight path, if this risk is confirmed, in such a way as to avoid such a collision, However, it can happen that the pilots do not react satisfactorily to the warning signals given by a collision warning device, at the risk of causing the destruction of the aircraft at the time of a collision with the terrain.
The patent U.S. Pat. No. 4,924,401 proposes a solution aimed at avoiding a collision of the aircraft with the terrain. This solution consists in defining a minimum altitude below which the aircraft must not descend and in piloting the aircraft automatically by means of the automatic pilot, when this minimum altitude is passed through whilst descending, in such a way as to command the aircraft to climb again and thus to prevent any collision with the terrain.
However, this known solution is above all adapted to the case where the pilot is unaware even though the aircraft is diving. Because of this, it has the disadvantage of acting very late on the flight path of the aircraft, and the action on this flight path is of course even greater because it is late. Consequently, in the case of a civil transport aircraft, this results in an uncomfortable situation and even a potential danger for the passengers.
Furthermore, the risk that this action on the flight path will not make it possible to protect the aircraft from a collision with the terrain is also high because of this late action.